How are somatosensory evoked potentials (SEPs) interpreted in comatose patients?

Updated: Feb 26, 2019
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In adults who are comatose following a cerebral anoxic insult (eg, due to a cardiopulmonary arrest), absence of the N20 (cortical) component of the median nerve SEP following stimulation of either median nerve predicts a bad outcome (death or persistent vegetative state) with virtually 100% specificity. [9] Preservation of the SEPs does not, however, ensure a good outcome, as patients may have extensive brain injury despite preservation of the afferent somatosensory pathways and primary somatosensory cortex, or they may die from other disease processes (eg, cardiac disease that caused the arrest). [10] On the other hand, presence of the N20 is a light predictor for good outcome. [11] In patients treated with targeted temperature management (TTM), absence of the SEPs may not predict poor outcome. [12, 13]

Bilateral absence of the N20 is also associated with poor outcomes in adult patients with coma due to traumatic brain injury, although some of these patients may recover consciousness if the absence of SEPs was due to a focal lesion that interrupted the pathway between the peripheral nerve and somatosensory cortex. Patients comatose from other causes such as infection and metabolic derangements may also have better outcomes despite bilateral absence of N20 on initial examination.

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